Therum is a distant but rich industrial world claimed by the humanSystems Alliance. Its plentiful heavy metals have fueled the recent manufacturing boom on Earth. Core samples rich with the fossils of simple silicon-based organisms indicate Therum was more habitable in the past than it is at present. Perhaps this explains the many Prothean ruins dotting the surface, most of which have been looted by mining corporations.

In the demo footage for Mass Effect, there was a mission on a planet named Caleston that involved rescuing a group of miners who had been trapped underground by the geth attack. This was later merged into the mission on Therum. The approach to the underground entrance and the battle outside are the same, but in the demo Shepard wanted to know why the geth would drop an Armature just to wipe out a group of miners, and decided the site was worth checking out.